In many applications, under specific conditions, means must be provided to permit thermal expansion and terminal motion of adjacent pipe sections. In certain instances, excessive reaction loading on the terminal equipment or upon the valves and other internal components introduces excessive stress on the piping system. In other cases, excessive pressure may also cause expansion of the pipes in a radial direction. Many times, because it is necessary to use the most direct routing for the pipes, there is insufficient flexibility in the pipe system. In situations such as these, expansion joints are frequently used.
Generally speaking, there are two basic types of expansion joints. The first is the sliding joint in which there is relative motion of adjacent parts and the second is the flexible joint in which there is no such relative motion but rather a distributed distortion of the device itself. Flexible joints are typically those depending on the elasticity of the material, bellows, or corrugated pipe. The present invention is of the sliding type of expansion joint in that it involves a particular configuration wherein various parts of the expansion joint configuration involves relative motion of adjacent parts and uses swivel joints and/or ball type joints.
It is well known that, due to heat and/or pressure, pipes tend to grow in length if both ends of the pipe are fixed. Under such conditions the pipe will buckle. If an expansion joint is used without an end load, then the pipe will see only a positive hoop stress and under pressure will create a negative longitudinal stress. A situation such as this may cause a buckling failure. An expansion joint that is capable of maintaining a full positive end load on the pipe at all times keeps the pipe line stable.